Method of manufacturing a rotor for an electric motor for a washing machine

ABSTRACT

A method of manufacturing a rotor for an electric motor that includes producing a generally flat metal strip, bending one section of the strip relative to another section, and rolling the strip to form a cup-shaped shell.

TECHNICAL FIELD

The present disclosure relates generally to an electric motor for awashing machine, and, more particularly, to a method of manufacturing arotor for an electric motor for a washing machine.

BACKGROUND

A washing machine is a domestic appliance for cleaning clothes, linens,and other laundry. A washing machine may include a tub and a drumpositioned in the tub that is sized to receive laundry for cleaning Thewashing machine may include an electric motor that causes the drum torotate relative to the tub during a washing operation. In some washingmachines, the electric motor may be connected to the drum via atransmission system including, for example, belts and pulleys. Theelectric motor may also be connected to the drum via a drive shaft.Washing machines including the latter type of electric motor are oftenreferred to as “direct drive” washing machines.

Electric motors typically include a stator and a rotor configured torotate relative to the stator. The stator may be fixed to the tub of thewashing machine and may include a number of stator coils. The rotor mayinclude one or more magnets that interact with the stator coils. Duringoperation, the stator coils may be sequentially energized withelectricity to cause the rotor to rotate.

In a direct drive washing machine, the rotor may be torsionally securedto the drive shaft so that drive force may be transferred to the drumvia the drive shaft.

SUMMARY

According to one aspect of the disclosure, a method of manufacturing arotor for an electric motor is disclosed. The method includes producinga generally flat metal strip including a plate having a firstlongitudinal end and a second longitudinal end, and a plurality ofprotrusions extending from the plate between the first longitudinal endand the second longitudinal end. The method also includes bending afirst section of the plate relative to a second section of the platealong an imaginary line extending between the first longitudinal end andthe second longitudinal end. The second section of the plate has theplurality of protrusions extending therefrom. The method includesrolling the plate about an imaginary axis to form a cup-shaped body thathas the plurality of protrusions extending radially inward and joiningthe first longitudinal end of the plate with the second longitudinal endof the plate. The method also includes attaching a hub that isconfigured to receive a drive shaft of the electric motor to theplurality of protrusions.

In some embodiments, each protrusion may include a body having a baseattached to the second section of the plate and a tip spaced apart fromthe base. Attaching the hub to the plurality of protrusions may includesecuring the hub to the tip of each protrusion.

In some embodiments, the method may also include bending a flangeextending from the body of a first protrusion to form a cooling finbetween the base and the tip of the first protrusion. In someembodiments, the method may also include embossing the first protrusionto form a groove in a first surface of the first protrusion.Additionally, in some embodiments, the method may include forming amounting hole through the tip of each protrusion. Attaching the hub tothe plurality of protrusions may include passing a fastener through themounting hole of each protrusion to secure the hub to the plurality ofprotrusions.

In some embodiments, attaching the hub to the plurality of protrusionsmay include molding a connecting flange of the hub to the tips of theplurality of protrusions. The connecting flange may be formed from apolymeric material.

Additionally, in some embodiments, joining the first longitudinal end ofthe plate with the second longitudinal end of the plate may includewelding the first longitudinal end and the second longitudinal end. Insome embodiments, joining the first longitudinal end of the plate withthe second longitudinal end of the plate may include positioning a tab,which extends from the first longitudinal end, in a notch defined in thesecond longitudinal end.

In some embodiments, producing the generally flat metal strip mayinclude producing a generally flat metal sheet having a first length.The generally flat metal sheet may include the generally flat metalstrip having a second length less than the first length, and a secondgenerally flat metal strip having a third length less than the firstlength. The second generally flat metal strip may include a second platehaving a first longitudinal end and a second longitudinal end, and asecond plurality of protrusions extending from the second plate.

In some embodiments, the method may also include attaching a pluralityof magnets to a first surface of the first section of the plate facingthe imaginary axis. Additionally, in some embodiments, the method mayinclude bending a third section of the plate relative to the secondsection of the plate along a second imaginary line extending between thefirst longitudinal end of the plate and the second longitudinal end ofthe plate prior to rolling the plate about the imaginary axis.

In some embodiments, the method may include forming an annular rib fromthe third section of the plate after rolling the plate about theimaginary axis. Additionally, in some embodiments, the method mayfurther include forming an annular groove in a first surface of thesecond section of the plate.

According to another aspect, a method of manufacturing a rotor for anelectric motor includes producing a generally flat metal strip includinga plate having a first longitudinal end and a second longitudinal end,and a plurality of protrusions extending from the plate. The method alsoincludes bending a first section of the plate relative to a secondsection of the plate along a first imaginary line extending between thefirst longitudinal end and the second longitudinal end. The secondsection of the plate has the plurality of protrusions extendingtherefrom in a first direction. The method includes bending a thirdsection of the plate relative to the first section along a secondimaginary line extending between the first longitudinal end and thesecond longitudinal end such that the third section extends in a seconddirection opposite the first direction. The method further includesrolling the plate about an imaginary axis such that the plurality ofprotrusions extend inwardly toward the imaginary axis, joining the firstlongitudinal end of the plate with the second longitudinal end of theplate, and attaching a hub to the plurality of protrusions. The hub isconfigured to receive a drive shaft of the electric motor.

In some embodiments, rolling the plate about the imaginary axis mayinclude forming a cup-shaped shell that includes the first section ofthe plate defining a substantially cylindrical outer wall of the shelland the second section of the plate defining a side wall of the shell.

In some embodiments, the method may include forming an annular groove ina first surface of the side wall of the plate. In some embodiments, themethod may include forming a mounting hole through each protrusion ofthe plurality of protrusions. Attaching the hub to the plurality ofprotrusions may include passing a fastener through the mounting hole ofeach protrusion to secure the hub to the plurality of protrusions.

In some embodiments, attaching the hub to the plurality of protrusionsmay include molding a connecting flange of the hub to the plurality ofprotrusions. In some embodiments, the method may also include bending afirst section of a first protrusion of the plurality of protrusionsrelative to a second section of the first protrusion to form a coolingfin.

According to another aspect, a method of manufacturing a rotor for anelectric motor includes producing a generally flat metal strip thatincludes a plate having a first longitudinal end and a secondlongitudinal end, and a plurality of protrusions extending from theplate. The method also includes forming a cup-shaped shell from themetal strip. The cup-shaped shell has the plurality of protrusionsextending radially inward. The method further includes joining the firstlongitudinal end of the plate with the second longitudinal end of theplate, and attaching a hub to the plurality of protrusions. The hub isconfigured to receive a drive shaft of the electric motor.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the following figures,in which:

FIG. 1 is a front perspective view of one embodiment of a rotor for anelectric motor;

FIG. 2 is a flow chart of a method of manufacturing the rotor of FIG. 1;

FIG. 3 is a top plan view of a metal strip produced according to themethod of FIG. 2;

FIG. 4 is a cross-sectional side elevation view of the metal strip afterbeing partially processed according to the method of FIG. 2;

FIG. 5 is a front perspective view of a shell formed from the metalstrip of FIGS. 3 and 4;

FIG. 6 is a partial cross-sectional side elevation view of the shellafter being further processed according to the method of FIG. 2; and

FIG. 7 is a front perspective view of one embodiment of a frame of therotor of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

While the concepts of the present disclosure are susceptible to variousmodifications and alternative forms, specific exemplary embodimentsthereof have been shown by way of example in the drawings and willherein be described in detail. It should be understood, however, thatthere is no intent to limit the concepts of the present disclosure tothe particular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

Referring now to FIG. 1, one embodiment of a rotor 10 for an electricmotor is shown. One example of an electric motor is shown and describedin U.S. Patent App. Pub. No. 2010/0307202, entitled “WASHING MACHINEWITH A DIRECT DRIVE SYSTEM,” which is incorporated herein by reference.The rotor 10 includes a hub 12 configured to be coupled to a drive shaft(not shown) of the electric motor and a frame 14 secured to the hub 12.A plurality of magnets 16 are secured to the frame 14.

The hub 12 of the rotor 10 includes a housing 18 that is secured to theframe 14 and a mounting collar 20 that is positioned in the housing 18.The housing 18 of the hub 12 includes a central platform 22 and aconnecting flange 24 extending outwardly from the platform 22. Aplurality of ribs 26 extend radially outward from the platform 22 toreinforce the structure of the housing 18. In the illustrativeembodiment, the housing 18 is formed from a polymeric material, such as,for example, a plastic resin. In other embodiments, the housing 18 mayalso be formed from a metallic material, such as, for example, aluminumor an aluminum alloy.

As shown in FIG. 1, the housing 18 is molded over the mounting collar 20via an injection molding process. In the illustrative embodiment, themounting collar 20 is formed from a metallic material, such as, forexample, steel. It should be appreciated that in other embodiments thehousing 18 may be formed separately from the mounting collar 20 andlater assembled with the mounting collar 20 to form the hub 12.Additionally, in other embodiments, the housing 18 and the collar 20 maybe formed as a single monolithic component.

The mounting collar 20 of the hub 12 includes a shell 30 that extendsoutwardly from the platform 22 of the housing 18. The shell 30 includesan outer face 32 that has a circular opening 34 defined therein. Aninner surface 36 extends inwardly from the opening 34 to define acylindrical passageway 38 through the collar 20. The mounting collar 20also includes a plurality of splines 40 that extend inwardly from theinner surface 36.

As shown in FIG. 1, the passageway 38 defines a longitudinal axis 42extending through the hub 12. The rotor 10 is configured to rotate aboutthe axis 42. When the rotor 10 is secured to the drive shaft, thesplines 40 are configured to engage the drive shaft of the electricmotor such that the rotor 10 may be torsionally secured to the driveshaft. In that way, rotation of the rotor 10 about the axis 42 causesrotation of the drive shaft of the motor.

As described above, the frame 14 of the rotor 10 is secured to the hub12. The frame 14 includes a side wall 50 and an outer rim 52 extendingfrom the side wall 50. In the illustrative embodiment, the frame 14 hasa cup-shape that is defined by the wall 50 and the rim 52, and the frame14 is formed as a single monolithic component from a metallic material,such as, for example, steel. It will be appreciated that in otherembodiments the frame 14 may be formed from aluminum or other metallicalloy.

As shown in FIG. 1, the side wall 50 of the frame 14 includes an annularwall section 54 and a plurality of spokes 56 that extend radially inwardfrom the annular wall section 54 toward the longitudinal axis 42. Theannular wall section 54 has an annular groove 180 defined therein thatis positioned adjacent to the intersection between the side wall 50 andthe outer rim 52. Each spoke 56 has a body 58 including a base 60 thatis connected to the annular wall section 54 and a tip 62 that is spacedradially inward from the base 60. The body 58 is tapered such that thebody 58 is wider at the base 60 than at the tip 62. The connectingflange 24 of the hub 12 is secured to the tip 62 of each spoke 56, asdescribed in greater detail below.

The body 58 of each spoke 56 has an inner surface 64, and a groove 66 isdefined in the inner surface 64. As shown in FIG. 1, the groove 66extends along the length of the body 58 between the base 60 and the tip62. It should be appreciated that in other embodiments each spoke 56 mayinclude additional grooves defined in different arrangements on theinner surface 64 of the spoke 56. Additionally, in other embodiments,the grooves may be omitted from one or more of the spokes 56.

The frame 14 of the rotor 10 further includes a plurality of coolingfins 70. Each cooling fin 70 includes a rectangular bar 72 that extendsfrom a side wall 74 of the body 58 of each spoke 56. As shown in FIG. 1,the bar 72 is positioned between the base 60 and the tip 62 of eachspoke 56. Each rectangular bar 72 includes an upper surface 86 that isoffset from, and extends parallel to, the inner surface 64 of the body58 of each spoke 56. When the rotor 10 is rotated about the longitudinalaxis 42, the cooling fins 70 assist in drawing air through the slots 88defined between the spokes 56. It should be appreciated that in otherembodiments the cooling fin may have an arched shape, a triangularshape, trapezoidal shape, or any other suitable configuration. It shouldalso be appreciated that in other embodiments the cooling fins may beomitted.

The rim 52 of the frame 14 includes an outer wall 90 extending from anend 92 attached to the side wall 50 to an end 94. The outer wall 90 hasan inner surface 96 that faces the longitudinal axis 42 of the rotor 10,and an outer surface 98 positioned opposite the inner surface 96. In theillustrative embodiment, the inner surface 96 is substantiallycylindrical. As shown in FIG. 1, the rim 52 has an annular rib 100 thatextends outwardly from the outer surface 98 of the wall 90 at the end94. It should be appreciated that in other embodiments the annular ribmay be omitted from the frame 14.

As described above, the rotor 10 also includes a plurality of magnets16. The magnets 16 are secured to the inner surface 96 of the outer wall90 of the rim 52. In the illustrative embodiment, each magnet 16 is apermanent magnet that generates a constant magnetic field in the rotor10. The magnets 16 may be formed from ferrite materials, alnico, orother metallic materials and may be produced by any known process,including, for example, sintering, molding, or extrusion. Duringoperation, the magnets 16 interact with the coils of the stator (notshown) to cause the rotor 10 to rotate about the longitudinal axis 42.

Referring now FIG. 2, a method of manufacturing the rotor 10 isillustrated. As shown in FIGS. 3-7, the rotor 10 may be manufactured byproducing a generally flat metal strip 112 and bending one section ofthe strip 112 relative to another section of the strip 112. The strip112 may be further processed to fashion the frame 14 of the rotor 10.Thereafter, the hub 12 and the magnets 16 may be attached to the frame14.

In block 210, the generally flat metal strip 112 may be produced via aprogressive stamping process. To do so, a metal strip or sheet 110 isadvanced through one or more stations of a progressive stamping die. Asthe sheet 110 is moved through the stations, the sheet 110 is cut intogenerally flat metal strips 112, 114. As shown in FIG. 3, the strip 114is mirror image of the strip 112. The sheet 110 has a substantiallyuniform thickness that may vary from approximately 1.0 millimeters to5.0 millimeters. While the sheet 110 is illustratively shown as the samelength as the strips 112, 114, it should be appreciated that the sheet110 may be part of a larger roll of sheet metal that is advanced throughthe stamping die and cut into one or more pieces.

The strip 112 includes a rectangular plate 116 extending from alongitudinal end 118 to another longitudinal end 120. The strip 112 alsoincludes a plurality of protrusions 122 that extend outwardly from asidewall 124 of the plate 116. As described in greater detail below,each protrusion 122 corresponds to a spoke 56 of the frame 14. Eachprotrusion 122 has a body 126 that includes a base 128 attached to thesidewall 124 of the plate 116 and a tip 130 spaced apart from the base128. The body 126 has a pair of tapered side walls 132, 134. Theprotrusion 122 also has a rectangular flange 136 that extends outwardlyfrom the sidewall 132 of the body 126.

The plate 116 of the strip 112 includes a pair of tabs 140 that extendoutwardly from the longitudinal end 118. A pair of notches 142 isdefined in the opposite longitudinal end 120 of the plate 116. Eachnotch 142 of the longitudinal end 120 is sized to receive acorresponding tab 140 of the longitudinal end 118 such that the ends118, 120 may be joined together, as described in greater detail below.It should be appreciated that in other embodiments the ends 118, 120 mayinclude additional tabs and/or slots. It should also be appreciated thatin other embodiments the tabs and slots may be omitted.

After the sheet 110 is cut into the strips 112, 114, the method 200advances to block 212 in which the strip 112 undergoes furtherprocessing. In block 212, the plate 116 is folded or bent along animaginary line 144 extending between the longitudinal ends 118, 120. Asshown in FIG. 3, the imaginary line 144 defines a plate section 146 anda plate section 148 of the plate 116, and the plurality of protrusions122 extend outwardly from the plate section 148. When the plate 116 isfolded, the plate section 146 is bent relative to the plate section 148,as shown in FIG. 4.

In block 212, the plate 116 is also folded or bent along anotherimaginary line 150 extending between the longitudinal ends 118, 120. Asshown in FIG. 3, the line 150 is positioned on the opposite side of theplate 116 from the line 144, and the line 150 defines another platesection 152 of the plate 116. When the plate 116 is folded along theline 150, the plate section 152 extends from the plate section 146 inthe direction opposite the plate section 148, as shown in FIG. 4. Anangle α is defined between the plate sections 146, 152. In theillustrative embodiment, the angle α has a magnitude less than ninetydegrees. It should be appreciated that the folding of the plate 116along the lines 144, 150 may be completed in one operation or inmultiple operations.

After folding the plate 116 in block 212, the method 200 may advance toblock 214 in which the strip 112 is processed into a generallycylindrical shell 160. To do so, the plate 116 may be curled or rolledabout an imaginary axis 162 such that the longitudinal end 118 isbrought into contact with the opposite longitudinal end 120. As shown inFIG. 5, the tabs 140 of the longitudinal end 118 are positioned in thenotches 142 of the longitudinal end 120. The ends 118, 120 are furtherjoined by welding the strip 112 along the seam 164 defined between theends 118, 120.

As shown in FIG. 5, the shape of the shell 160 corresponds to thecup-shape of the frame 14. The plate section 146 defines the outer rim52 and an outer diameter 164 of the shell 160. The plate section 148,which extends inwardly from the plate section 146, defines the annularwall section 54. The plurality of protrusions 122 extend radially inwardfrom the plate section 148 toward the axis 162. As described above, eachprotrusion 122 corresponds to a spoke 56 of the frame 14. After rollingthe plate 116 about the imaginary axis 162 and joining the ends 118,120, the method 200 may advance to block 216.

In block 216, the shell 160 undergoes further processing to calibratethe diameter of the shell 160 and reinforce the shell 160. To calibratethe diameter, the inner diameter 164 of the shell 160 may be measured.If the diameter 164 is incorrect, the plate section 146 may be adjustedto increase or decrease the diameter 164. To do so, the diameter 164 ofthe shell 160 may be expanded by plastic deformation and measured againto determine if the shell 160 has the target final inner diameter.

Additionally, in block 216, the shell 160 is reinforced by bending theplate section 152 in the direction indicated by arrow 170 in FIG. 6. Theplate section 152 is curled into a U-shape, thereby defining the annularrib 100. As shown in FIG. 6, an end 172 of the plate section 152 ispositioned over the outer surface 174 of the plate section 146. Itshould be appreciated that in other embodiments the section 152 mayextend perpendicularly from the section 146 or at an angle relative tothe section 146.

As shown in FIGS. 6 and 7, an annular groove 180 is defined in the platesection 148 in block 216. To form the groove 180, the plate section 148is pressed in the direction indicated by arrow 182 to emboss the groove180 into the inner surface 186 of the plate section 148. In thisoperation, any number of machines may be used to create the groove 180,including, for example, a pressure embossing machine having matched maleand female dies.

The method 200 may then advance to block 218 in which grooves are addedto the shell 160. As shown in FIG. 6, the surface 64 of each protrusion122 (or spoke 56) is embossed to define a groove 66 in the surface 64.To do so, the protrusion 122 is pressed in the direction indicated byarrow 176. Any number of machines may be used to create the groove 66,including, for example, a pressure embossing machine having matched maleand female dies. As described above, the groove 66 extends along thelength of the protrusion 122.

After forming the grooves 66 in the shell 160, the method 200 mayadvance to block 220 in which the cooling fins 70 are formed in theshell 160. As described above, each protrusion 122 has a flange 136 thatextends outwardly from the sidewall 132 of the body 126. As shown inFIG. 5, each flange 136 includes a side surface 184 that is co-planarwith the surface 64 of the protrusion 122 (or spoke 56). To form acooling fin 70, the flange 136 is bent relative to the body 126 of theprotrusion 122, as indicated by arrow 188 in FIG. 5. When the flange 136is in properly positioned as shown in FIG. 7, the side surface 184 ofthe flange 136 extends orthogonal to the surface 64 of the protrusion122, and the flange 136 defines the cooling fin 70. The bendingoperation may be repeated for each protrusion 122 until each flange 136is positioned as shown in FIG. 7. It should be appreciated that theblocks 216 through 220 may be performed in a single operation or may beseparated into multiple operations.

As shown in FIG. 7, the shell 160 includes the features of the frame 14.The plate section 146 defines the outer rim 52 of the frame 14, and theplate section 148, which extends inwardly from the plate section 146,defines the annular wall section 54. The plurality of protrusions 122extend radially inward from the plate section 148 and define the spokes56 of the frame 14. It should be appreciated that in other embodimentsone or more the operations described in the method 200 may be altered oromitted. For example, where the frame does not include cooling fins,block 220 may be omitted. Similarly, for embodiments in which the frameincludes additional grooves or reinforcing structure, additionaloperations may be added. Additionally, it should be appreciated that theorder of the operations shown and described in reference to FIGS. 2-7 isintended to be exemplary and may be altered in other embodiments.

The method 200 may then advance to block 222 in which the hub 12 and themagnets 16 are attached to the frame 14. As described above, the magnets16 are attached to the surface 96 of the rim 52 of the frame 14. To doso, an adhesive may be applied to the surface 96 and/or the back surface(not shown) of each magnet 16. As shown in FIG. 1, each magnet 16 isinstalled along the inner circumference of the rim 52. The magnets 16are positioned end-to-end on the surface 96.

In block 222, the hub 12 is secured to the frame 14. As described above,the hub 12 includes a housing 18 and a mounting collar 20. In theillustrative embodiment, the housing 18 is molded over the mountingcollar 20 and the tips 62 of the spokes 56 via an injection moldingprocess. To do so, the collar 20 and the frame 14 may be placed in amold. A polymeric or plastic material is injected into the mold andflows over the tips 62 of the spokes 56 and the mounting collar 20. Whenthe material cools, the housing 18 is formed, thereby securing themounting collar 20 to the frame 14.

It should be appreciated that in other embodiments the hub 12 may besecured to the frame 14 via a number of fasteners. To do so, the tip 62of each spoke 56 may have a pair of through-holes 190, 192 definedtherein, as shown in FIG. 7. The through-holes 190, 192 of the spokes 56may be sized to receive fasteners, such as, for example, pins, tabs, orbolts that secure the hub 12 to the frame 14. It should be appreciatedthat the hub 12 may be secured to the frame 14 before or after themagnets 16 are attached to the frame 14.

There are a plurality of advantages of the present disclosure arisingfrom the various features of the method, apparatus, and system describedherein. It will be noted that alternative embodiments of the method,apparatus, and system of the present disclosure may not include all ofthe features described yet still benefit from at least some of theadvantages of such features. Those of ordinary skill in the art mayreadily devise their own implementations of the method, apparatus, andsystem that incorporate one or more of the features of the presentinvention and fall within the spirit and scope of the present disclosureas defined by the appended claims.

1. A method of manufacturing a rotor for an electric motor, comprising:producing a generally flat metal strip that includes (i) a plate havinga first longitudinal end and a second longitudinal end, and (ii) aplurality of protrusions extending from the plate between the firstlongitudinal end and the second longitudinal end, bending a firstsection of the plate relative to a second section of the plate along animaginary line extending between the first longitudinal end and thesecond longitudinal end, the second section of the plate having theplurality of protrusions extending therefrom, rolling the plate about animaginary axis to form a cup-shaped body, the cup-shaped body includingthe plurality of protrusions extending radially inward, joining thefirst longitudinal end of the plate with the second longitudinal end ofthe plate, and attaching a hub to the plurality of protrusions, the hubbeing configured to receive a drive shaft of the electric motor.
 2. Themethod of claim 1, wherein each protrusion includes a body having a baseattached to the second section of the plate and a tip spaced apart fromthe base, and attaching the hub to the plurality of protrusions includessecuring the hub to the tip of each protrusion.
 3. The method of claim2, further comprising bending a flange extending from the body of afirst protrusion to form a cooling fin between the base and the tip ofthe first protrusion.
 4. The method of claim 3, further comprisingembossing the first protrusion to form a groove in a first surface ofthe first protrusion.
 5. The method of claim 2, further comprisingforming a mounting hole through the tip of each protrusion, whereinattaching the hub to the plurality of protrusions includes passing afastener through the mounting hole of each protrusion to secure the hubto the plurality of protrusions.
 6. The method of claim 2, whereinattaching the hub to the plurality of protrusions includes molding aconnecting flange of the hub to the tips of the plurality ofprotrusions, the connecting flange being formed from a polymericmaterial.
 7. The method of claim 1, wherein joining the firstlongitudinal end of the plate with the second longitudinal end of theplate includes welding the first longitudinal end and the secondlongitudinal end.
 8. The method of claim 1, wherein joining the firstlongitudinal end of the plate with the second longitudinal end of theplate includes positioning a tab extending from the first longitudinalend in a notch defined in the second longitudinal end.
 9. The method ofclaim 1, wherein producing the generally flat metal strip includesproducing a generally flat metal sheet having a first length, thegenerally flat metal sheet comprising: the generally flat metal striphaving a second length less than the first length, and a secondgenerally flat metal strip having a third length less than the firstlength, the second generally flat metal strip including: (i) a secondplate having a first longitudinal end and a second longitudinal end, and(ii) a second plurality of protrusions extending from the second plate.10. The method of claim 1, further comprising attaching a plurality ofmagnets to a first surface of the first section of the plate, the firstsurface facing the imaginary axis.
 11. The method of claim 1, furthercomprising bending a third section of the plate relative to the secondsection of the plate along a second imaginary line extending between thefirst longitudinal end of the plate and the second longitudinal end ofthe plate prior to rolling the plate about the imaginary axis.
 12. Themethod of claim 11, further comprising forming an annular rib from thethird section of the plate after rolling the plate about the imaginaryaxis.
 13. The method of claim 1, further comprising forming an annulargroove in a first surface of the second section of the plate.
 14. Amethod of manufacturing a rotor for an electric motor, comprising:producing a generally flat metal strip that includes (i) a plate havinga first longitudinal end and a second longitudinal end, and (ii) aplurality of protrusions extending from the plate, bending a firstsection of the plate relative to a second section of the plate along afirst imaginary line extending between the first longitudinal end andthe second longitudinal end, the second section having the plurality ofprotrusions extending therefrom in a first direction, bending a thirdsection of the plate relative to the first section along a secondimaginary line extending between the first longitudinal end and thesecond longitudinal end such that the third section extends in a seconddirection opposite the first direction, rolling the plate about animaginary axis such that the plurality of protrusions extend inwardlytoward the imaginary axis, joining the first longitudinal end of theplate with the second longitudinal end of the plate, and attaching a hubto the plurality of protrusions, the hub being configured to receive adrive shaft of the electric motor.
 15. The method of claim 14, whereinrolling the plate about the imaginary axis includes forming a cup-shapedshell that includes the first section of the plate defining asubstantially cylindrical outer wall of the shell and the second sectionof the plate defining a side wall of the shell.
 16. The method of claim15, further comprising forming an annular groove in a first surface ofthe side wall of the plate.
 17. The method of claim 14, furthercomprising forming a mounting hole through each protrusion of theplurality of protrusions, wherein attaching the hub to the plurality ofprotrusions includes passing a fastener through the mounting hole ofeach protrusion to secure the hub to the plurality of protrusions. 18.The method of claim 14, wherein attaching the hub to the plurality ofprotrusions includes molding a connecting flange of the hub to theplurality of protrusions.
 19. The method of claim 14, further comprisingbending a first section of a first protrusion of the plurality ofprotrusions relative to a second section of the first protrusion to forma cooling fin.
 20. A method of manufacturing a rotor for an electricmotor, comprising: producing a generally flat metal strip that includes(i) a plate having a first longitudinal end and a second longitudinalend, and (ii) a plurality of protrusions extending from the plate,forming a cup-shaped shell from the metal strip, the cup-shaped shellhaving the plurality of protrusions extending radially inward, joiningthe first longitudinal end of the plate with the second longitudinal endof the plate, and attaching a hub to the plurality of protrusions, thehub being configured to receive a drive shaft of the electric motor.